Hybrid Lithium-ion Capacitor / Lithium-ion Battery System for Extended Performance

The proposed task will involve the design of a hybrid power system with lithium-ion (li-ion) capacitors (LICs), li-ion batteries and solar cells. The challenge in energy storage for long-term space missions is to obtain greater than 230 Wh/kg that equates to providing power for the EVA suit and surface systems for a minimum of eight hours. Although the current EMU li-ion battery provides power for 8 hours, it weighs about 6 kg and is only one of four battery systems providing power for various applications. The new advanced suit will include, apart from the existing power demands, an array of biological sensors and monitors and a high-tech video system with a mass limit on the battery of less than 5 kg. No battery-only system can currently provide this capability for a continuous 8 hour period, even with the advanced silicon-based anodes being studied in the battery industry today. Working on human-rated space technology requires higher safety goals which, we believe, this system will provide.

The work focused on testing the Li-ion supercapacitors to confirm their performance and safety.  The li-ion supercaps were found to be safe under several off-nominal conditions such as overcharge, overdischarge into reversal, external short and simulated internal short.  The li-ion supercaps were found to hold charge for the three month period tested and showed insignificant loss in capacity after that hold period.  The li-ion supercaps were found to have the capability to accept charge quickly from a power supply.  The testing to provide controlled current from the supercapacitors to the battery was not completed due to lack of personnel to carry out the testing.  With the help of an intern this Fall, that work will be completed.